Various pouches formed by working various laminated structures each formed by laminating various kinds of sheets are used principally as packaging articles. Recently, lithium batteries each formed by packaging a lithium battery module in a pouch formed from a laminated structure have been developed.
A lithium battery module, which is also called a lithium secondary battery module, employs a polyelectrolyte, generates current by the agency of the migration of lithium ions and have positive and negative electrodes containing polymers as active substances.
The lithium battery comprises a lithium battery module having a positive electrode collector (aluminum or nickel), a positive electrode active substance layer (metal oxide, carbon black, a metal sulfide, an electrolytic solution or a polymer, such as polyacrylonitrile), an electrolytic layer (a carbonate electrolytic solution of propylene carbonate, ethylene carbonate, dimethyl carbonate or ethylene methyl carbonate, an inorganic solid electrolyte of a lithium salt or a gelled electrolyte), a negative electrode active layer (lithium, an alloy, carbon, a liquid electrolyte or a polymer, such as polyacrylonitrile) and a negative collector (copper, nickel or a stainless steel), and a package containing the lithium battery module therein.
The lithium battery is used as a power supply for personal computers, portable terminal devices, such as portable telephones and PDAs, video cameras, electric vehicles, robots, artificial satellites and the like and as an energy storage battery.
The lithium battery comprises a lithium battery module having a positive collector of aluminum or nickel, a positive electrode active substance layer of a metal oxide, carbon black, a metal sulfide, an electrolytic solution or a polymer, such as polyacrylonitrile, an electrolytic layer of a carbonate electrolytic solution of propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl carbonate or ethylene methyl carbonate, an inorganic solid electrolyte containing a lithium salt or a gelled electrolyte, a negative electrode active layer of lithium, an alloy, carbon, a liquid electrolyte or a polymer, such as polyacrylonitrile, and a negative collector of copper, nickel or a stainless steel, and a package containing the lithium battery module therein.
The package of the lithium battery is a cylindrical or parallelepipedic metal can formed by pressing a metal sheet or a pouch formed by working a multilayer film consisting of an outer layer, an aluminum layer and a sealant layer.
These packages for the lithium batteries have the following problems. The metal can has rigid walls and hence the shape of the lithium battery module is dependent on that of the metal can. Since the hardware is designed so as to conform to the shape of the battery pack, the dimensions of the hardware are dependent on the shape of the battery pack, which reduces the degree of freedom of designing the shape of the hardware.
The pouch made from a multilayer film does not place any restrictions on the shape of the hardware using the battery pack like the metal can does. However, there have not yet been developed any packaging laminated structures satisfactorily meeting physical properties and functions required of materials of packages for the lithium battery. The required physical properties and functions include the followings.
For example, the package for the lithium battery must be capable of hermetically sealing portions of electrodes connecting a principal part of the lithium battery module to hardware to insulate the same from the atmosphere. Therefore, the innermost layer of the multilayer film must be capable of adhering to the electrodes, particularly, must be capable of adhering to the electrodes when heat and pressure are applied thereto.
The lithium battery must be capable of maintain the sealing effect even if the temperature of the lithium battery module rises during charging and discharging, and must be, as well as hardware that withstands high temperatures, such as high temperatures on the instrument panel of a vehicle in summer, and low temperatures in a cold district, must be heat-resistant and cold-resistant. The lithium battery must be capable of maintaining satisfactory sealing effect in a severe environment.
Sometimes, it occurred that the electrolyte of the lithium battery module consisting of a carbonate solvent and a lithium salt affects adversely to the package and reduces bond strength between the layers of the multilayer film. The solvent (carbonate solvent) contained in the lithium battery module swells adhesive layers bonding together the component layers of the multilayer film to reduce bond strength between the layers.
It is possible that an acid is produced and heat is generated by the hydrolysis of the electrolyte, a metal barrier layer is corroded by the agency of the acid and heat to reduce bond strength between the layers, and that the battery is ignited by the heat. If the temperature of the battery rises, the electromotive force of the battery decreases and it is possible that the device connected to the battery stops or malfunctions.
The electrolysis of the electrolyte that causes those problems is caused by the penetration of external moisture into the sealed system of the battery. Therefore, the package must have a barrier property capable of inhibiting the penetration of external moisture into the package.
Packages containing batteries including lithium batteries must not be conductive and must not transmit electricity to devices (hardware) surrounding the packages and must be capable of electrically isolating the electrodes from each other so that the electrodes are not short-circuited.
The package of the lithium battery may be a metal can, a pouch or a formed package having a container and a cover. When the formed package having the containing part and the cover is employed, a resin forming the innermost layer of the laminated structure must be heat-adhesive and the laminated structure for forming the formed package must have a high formability.